As a contractor moving from project to project, I have found following useful to gain historical perspective of any agency / department etc..
Knowledge Management Systems, Enterprise Architecture, Standard Operating Procedures, Self Start Tool Kit, eLearning are all tools applied to bring a new employee up-to speed.
Especially in the CIO office following documents have been useful
Agency Vision Document
CIO Vision Document
Enterprise Transition Plan
Agency Modernization Plan
Investment Plan etc
When there were few number of employees joining together
Workshop and presentation conducted by the group head along with the key managers responsible for programs / projects / domains etc, have been very effective in providing perspective on the past efforts and also regarding the vision for the future plans / directions